This invention relates to a contact structure to establish electrical connection with contact targets such as contact pads on semiconductor devices, and more particularly, to a contact structure formed with a flexible cable for use with a probe contact assembly to test semiconductor wafers, IC chips and the like, with high speed, high density and low cost.
In testing high density and high speed electrical devices such as LSI and VLSI circuits, a high performance contact structure provided on a probe card must be used. A contact structure is basically formed of a contact substrate (space transformer) having a large number of contactors or probe elements. The contact substrate is mounted on a probe card for testing LSI and VLSI chips, semiconductor wafers, burn-in of semiconductor wafers and dice, testing and burn-in of packaged semiconductor devices, printed circuit boards and the like.
In the case where semiconductor devices to be tested are in the form of a semiconductor wafer, a semiconductor test system such as an IC tester is usually connected to a substrate handler, such as an automatic wafer prober, to automatically test the semiconductor wafer. Such an example is shown in FIG. 1 in which a semiconductor test system has a test head 100 which is ordinarily in a separate housing and electrically connected to the test system with a bundle of cables 110. The test head 100 and a substrate handler 400 are mechanically as well as electrically connected with one another with the aid of a manipulator 500 which is driven by a motor 510. The semiconductor wafers to be tested are automatically provided to a test position of the test head 100 by the substrate handler 400.
On the test head 100, the semiconductor wafer to be tested is provided with test signals generated by the semiconductor test system. The resultant output signals from the semiconductor wafer under test (IC circuits formed on the semiconductor wafer) are transmitted to the semiconductor test system. In the semiconductor test system, the output signals are compared with expected data to determine whether the IC circuits on the semiconductor wafer function correctly or not.
In FIG. 1, the test head 100 and the substrate handler 400 are connected through an interface component 140 consisting of a performance board 120 (shown in FIG. 2) which is a printed circuit board having electric circuit connections unique to a test head""s electrical footprint, coaxial cables, pogo-pins and connectors. In FIG. 2, the test head 100 includes a large number of printed circuit boards 150 which correspond to the number of test channels (test pins) of the semiconductor test system. Each of the printed circuit boards 150 has a connector 160 to receive a corresponding contact terminal 121 of the performance board 120. A xe2x80x9cfrogxe2x80x9d ring 130 is mounted on the performance board 120 to accurately determine the contact position relative to the substrate handler 400. The frog ring 130 has a large number of contact pins 141, such as ZIF connectors or pogo-pins, connected to contact terminals 121, through coaxial cables 124.
As shown in FIG. 2, the test head 100 is placed over the substrate handler 400 and mechanically and electrically connected to the substrate handler through the interface component 140. In the substrate handler 400, a semiconductor wafer 300 to be tested is mounted on a chuck 180. In this example, a probe card 170 is provided above the semiconductor wafer 300 to be tested. The probe card 170 has a large number of probe contactors (such as cantilevers or needles) 190 to contact with contact targets such as circuit terminals or contact pads in the IC circuit on the semiconductor wafer 300 under test.
Electrical terminals or contact pads of the probe card 170 are electrically connected to the contact pins (pogo-pins) 141 provided on the frog ring 130. The contact pins 141 are also connected to the contact terminals 121 of the performance board 120 with the coaxial cables 124 where each contact terminal 121 is connected to the printed circuit board 150 of the test head 100. Further, the printed circuit boards 150 are connected to the semiconductor test system through the cable 110 having, for example, several hundreds of inner cables.
Under this arrangement, the probe contactors 190 contact the surface (contact targets) of the semiconductor wafer 300 on the chuck 180 to apply test signals to the semiconductor wafer 300 and receive the resultant output signals from the wafer 300. The resultant output signals from the semiconductor wafer 300 under test are compared with the expected data generated by the semiconductor test system to determine whether the IC circuits on the semiconductor wafer 300 performs properly.
FIG. 3 is a cross sectional view showing an example of structure of a probe contact system formed with a pin block 130, a probe card 60, and a contact structure 10. Typically, the contact structure 10 is formed of a contact substrate (space transformer) 20 having a large number of contactors 30. In the example of FIG. 3, the probe contact system further includes a conductive elastomer 50 between the probe card 60 and the contact structure 10. FIG. 3 further shows a semiconductor wafer 300 having contact pads 320 thereon as contact targets. The pin block 130 and probe card 60 in FIG. 3 respectively correspond to the pogo-pin block (frog ring) 130 and probe card 170 in FIG. 2.
The pin block 130 has a large number of pogo-pins (contact pins) 141 to interface between the probe card 60 and the performance board 120 (FIG. 2). At upper ends of the pogo-pins 141, cables 124 such as coaxial cables are connected to transmit signals to printed circuit boards (pin cards) 150 in the test head 100 in FIG. 2 through the performance board 120.
The probe card 60 has a large number of contact pads (pogo-pin pads) 65 on the upper surface and contact pads 62 on the lower surfaces thereof. The contact pads 62 and 65 are connected through interconnect traces 63 to fan-out the pitch of the contact structure to match the pitch of the pogo-pins 141 on the pogo-pin block 130.
The conductive elastomer 50 is to ensure electrical communications between the electrodes 22 of the contact structure and the electrodes 62 of the probe card by compensating unevenness or vertical gaps therebetween. The conductive elastomer 50 is an elastic sheet having a large number of conductive wires in a vertical direction. For example, the conductive elastomer 50 is comprised of a silicon rubber sheet and a multiple rows of metal filaments. The metal filaments (wires) are provided in the vertical direction of FIG. 3, i.e., orthogonal to the horizontal sheet of the conductive elastomer 50.
As shown in FIG. 3, the contact structure 10 is basically formed of the contact substrate (space transformer) 20 and a plurality of contactors 30. The contact structure 10 is so positioned over the contact targets such as contact pads 320 on a semiconductor wafer 300 to be tested that the contactors 30 establish electric connections with the semiconductor wafer 300 when pressed against each other. Although only two contactors 30 are shown in FIG. 3, a large number, such as several hundreds or several thousands of contactors 30 are aligned on the contact substrate 20 in actual applications such as semiconductor wafer testing.
The contactors 30 in this example have a beam or finger like shape having a conductive layer 35 made through a semiconductor production process including, for example, photolithography and electroplating processes on a silicon substrate. The contactors 30 can be directly mounted on the contact substrate 20 as shown in FIG. 3 and to form the contact structure 10 which then can be mounted on the probe card 60 through the conductive elastomer 50. Since the contactors 30 can be fabricated in a very small size, such as 50 xcexcm pitch, an operable frequency range of a contact structure or probe card mounting the contactors 30 can be in the range of 2 GHz or higher.
An interconnect trace 24 is connected to the conductive layer 35 at the bottom of the contact substrate (space transformer) 20. The contact substrate 20 further includes a via hole 23 and an electrode 22. The electrode 22 is to interconnect the contact substrate 20 to an external structure such as the contact pads 62 and 65 of the probe card 60 through the conductive elastomer. Thus, when the semiconductor wafer 300 moves upward, the silicon finger contactors 30 and the contact targets 320 on the wafer 300 mechanically and electrically contact with each other. Consequently, a signal path is established from the contact target 320 to a test head of the semiconductor test system through the electrodes 22 on the contact substrate 20, conductive elastomer 50, probe card 60 and pin block 130.
FIG. 4 is a cross sectional view of another example of contact assembly. The contact substrate (space transformer) 20 having a plurality of contactors 30 is mounted on the probe card 60 through a support frame 55 and a conductive elastomer 50. The support frame 55 for supporting the contact substrate 20 is connected to the probe card 60 by fastening means such as screws 150 and 152. As noted above, the conductive elastomer 50 establishes electrical conductivity only in the vertical direction, i.e., between the contact substrate 20 and the probe card 60. The probe card 60 has contact pads 65 for electrical connection with pogo-pins 141 when fully assembled.
In the foregoing conventional example, a large number of contactors must be used in the semiconductor wafer test, such as from several hundreds to several thousands. Because such a large number of contactors are needed in the contact structure, the resultant contact structure involves high production cost. Since the semiconductor industry is under the continued demands of improving performance per cost, it is also necessary to decrease the test cost using the semiconductor test system. Under the circumstances, there is a need in the industry to incorporate a more simple and economical way to form the contact structure for testing a semiconductor wafer or IC chips.
Therefore, it is an object of the present invention to provide a contact structure and a probe contact assembly to establish electrical contact with contact targets with low cost and high performance.
It is another object of the present invention to provide a contact structure and a probe contact assembly having a flexible cable and contactors formed at one end of the flexible cable for establishing electrical communication with contact targets with high frequency range, density and and low cost.
It is a further object of the present invention to provide a contact structure and a probe contact assembly using a flexible cable for establishing signal paths between contactors and contact pads on a probe card to eliminate a space transformer or fine patterns on the space transformer thereby reducing the cost of the probe contact assembly.
In the present invention, the contact structure includes a probe card having a plurality of sockets and a plurality of contact pads and signal patterns for connecting the sockets and the contact pads, a plurality of contactors mounted on the probe card in a manner that tips of the contactors are projected from one surface of the probe card to contact with the contact targets, and a flexible cable having a plurality of signal patterns for transmitting electrical signals therethrough wherein the flexible cable has the contactors at one end while being connected to the sockets on the probe card at another end.
The contactors are integrally formed at the end of the flexible cable using conductor of the signal patterns on the flexible cable. Alternatively, the contactors are produced separately from the flexible cable and attached to the corresponding signal patterns on the flexible cable. The flexible cable having the contactors are provided on one surface of the probe card and the tips of the contactors are inserted in the probe card and projected from another surface of the probe card. Preferably, the flexible cable having the contactors is clamped by an alignment frame and attached to the probe card after inserting the contactors in the probe card.
In a further aspect, the contact structure of the present invention includes a probe card having a plurality of sockets and a plurality of contact pads and signal patterns for connecting the sockets and the contact pads, a support substrate provided in parallel with the probe card for mounting contactors for connecting the contactors with the contact targets, a plurality of contactors mounted on the support substrate in a manner that tips of the contactors are projected from one surface of the support substrate to contact with the contact targets, and a flexible cable having a plurality of signal patterns for transmitting electrical signals therethrough wherein the flexible cable has the contactors at one end while being connected to the sockets on the probe card at another end.
Further aspect of the present invention is a probe contact assembly for interfacing between semiconductor device under test and a semiconductor test system. The probe contact assembly includes the contact structure noted above in addition to a plurality of flexible contact pins for connecting the contact pads on the probe card with the semiconductor test system thereby sending test signals to the semiconductor device under test.
According to the present invention, the contact structure is created with use of flexible flat cables which are available in the market. The contactors are formed at one end of the flexible cable and are mounted on a probe card or support substrate. The contact structure of the present invention is low cost, reliable and yet achieves high performance. Since the flat cables connecting the contactors and the pads on the probe card enable to obviate either a space transformer (contact substrate) or fine pitch wiring patterns on the contact substrate in the conventional technology, the present invention also contributes to the overall cost reduction and design simplification in the probe contact assembly.